This invention relates to automated inspection apparatus and more specifically to apparatus for automatically inspecting apertured material. Even more particularly, this invention relates to an automatically operated apparatus for inspecting aperture masks for eventual utilization in color television cathode ray tubes.
The conventional aperture mask found in most color television cathode ray tubes is positioned within the envelope of the tube in spaced relationship to an adjacent cathodoluminescent screen formed on the inner surface of the tube face panel. The primary reason for the mask is to insure that electron beams emitted from electron guns positioned in the neck of the tube strike the proper phosphor dots found in the cathodoluminescent screen to provide the correct color combinations while not allowing the electron beams to overlap and strike other dots.
Aperture masks, as described above, are made from sheets of very thin metal, usually steel, and contain thousands of very small apertures or holes through which the electron beams are passed before striking the phosphor dots. These holes are usually etched out of the metal through the employment of photographic and etching techniques standard in the industry. After photoprinting the hole pattern onto the mask surfaces, the etching solutions are sprayed on to remove the exposed areas. After etching, the masks are still integral parts of a long metal strip or web. Individual masks are cut from this strip and formed to coincide with the internal portion of the cathode ray tube screen.
Typical examples of the sizes of holes in aperture masks may range from 0.005 to 0.014 inch and have center to center spacings ranging from 0.02 to 0.03 inch depending on the overall size of the mask and corresponding picture tube. Additionally, many of the newer varieties of today's picture tubes employ masks having elongated or slotted apertures therein.
It can be readily seen, therefore, that the size of these apertures are critical in order that proper electron beam-phosphor dot combinations occur. To assure that these critical dimensions are maintained during the manufacture of these masks, various methods of inspection have been employed. One such method has been for a human inspector to examine the mask, utilizing some means of magnification. Not only has this method proven time consuming, but the possibility for human error is ever present. A further more advanced method of inspection has been to employ a frame having several reading heads which read various points on the masks as they move on the production line. While substantially eliminating the human error possibility, this method also requires undesirable time consumption, primarily because it is necessary to clamp each of these reading heads to the masks at these points. Still another method is illustrated in U.S. Pat. No. 3,744,905 wherein a pair of light detectors receives the light transmitted through the moving mask line by a corresponding pair of light sources positioned on an opposite side of the line. While this apparatus serves effectively to calibrate the aperture sizes in the mask over a broad range, it is incapable of selectively monitoring aperture sizes at several designated locations on the mask without requiring substantial modification. When utilizing the plural nozzle etching sprayers typically found in today's aperture mask production, this selective capability by the inspecting apparatus would in turn permit adjustment to only one or a few of the etchers, thus providing a more precisioned end product.
It is believed therefore that an apparatus and method capable of automatically inspecting designated areas on apertured material to determine the relative sizes of the apertures within said material would constitute an advancement in the art.